Method of making a BicMOS device

Abstract: A merged BiCMOS device 10 having a bipolar transistor 60 and a PMOS transistor 64 formed in the same well region 18a. Bipolar transistor 60 is comprised of an emitter electrode 30, base region 26, and collector region formed by well region 18b. Emitter electrode 30 is separated from base region 26 by thick oxide 24. PMOS transistor 64 comprises source/drain regions 52 and 52a, gate electrode 40, and gate oxide 36. PMOS transistor 64 may also comprises LDD regions 44. Source/drain region 52a is in contact with base region 26. If desired, the emitter electrode 30 and gate electrode 40 may be silicided. The PMOS transistor gate oxide 36 is grown after depositing the emitter electrode 30.

Description: FIELD OF THE INVENTION This invention generally relates to semiconductor processing and more specifically to BiCMOS processes. BACKGROUND OF THE INVENTION The integration of MOSFET structures and bipolar transistors on a single substrate has become very desirable. As is well known in the art, digital and linear functions are often performed by integrated circuits using either bipolar or metal-oxide semiconductor (MOS) technology. Bipolar integrated circuits, of course provide higher speed operation and greater drive currents than the MOS circuits, at the cost of higher power dissipation, especially when compared against complementary MOS (CMOS) circuits. Advances in manufacturing technology have allowed the use of both bipolar and CMOS transistors in the same integrated circuit (commonly referred to as BiCMOS devices). Further exploitation of the high current driving capabilities of the bipolar transistor is important to obtaining even higher levels of bipolar or merged bipolar CMOS integration. Bipolar transistors are typically formed by using a moat region for the base of the bipolar transistor, doped polysilicon for the emitter, and a well region for the collector. Additional moat regions are then used to form any Schottky diodes or source/drain regions of PMOS transistors. In the proceedings of the IEEE Bipolar Circuits and Technology Meeting, September 1990 (pages 78 to 81) W. R. Burger et al. report on a complementary BiCMOS (CBiCMOS) process offering improved drive capability and low voltage performance by integration of a poly emitter vertical PNP transistors into a core BiCMOS technology containing NPN bipolar and CMOS transistors. Bipolar devices are formed subsequently to NMOS and PMOS devices in the wells over the buried layers used by the NMOS and the PMOS circuit elements. The process features two electrode layers and two underlying insulator layers. EP-A-0 436 297 shows a BiCMOS device with a structure in which the inactive base of a bipolar transistor and the drain of a CMOS transistor are formed by one doped region and in which the collector of the bipolar transistor and the source of the CMOS transistor are made contiguous. Other BiCMOS processes with integrated device modules like a short key barrier diode or a lateral PNP transistor are disclosed in JP-A-61136255 and in the Proceedings of the IEEE 1990 Bipolar Circuits and Technology Meeting (pages 154 to 157) by Ali Iranmanesh et al. SUMMARY OF THE INVENTION Generally, and in one form of the invention, a method for forming a semiconductor device is defined in the claims. A first insulator layer is formed over a surface of a semiconductor body having a well region. The base region is implanted through the first insulation layer in a first portion of the well region. Next, an emitter electrode is formed over the first insulator layer and the base region. A portion of the emitter electrode extends through the first insulator layer to the base region. The exposed portion of the first insulator layer is removed. Next, a second insulator layer is grown on the surface of the semiconductor body. The growing step also serves as an emitter anneal. A plurality of gate electrodes is then formed on the second insulator layer. At least one gate electrode is formed over the first well region. A plurality of source/drain regions are formed at a temperature less than 900°C at the surface of the semiconductor body. One of the source/drain regions is formed in the well region between the gate electrode and the emitter electrode. This source/drain region is in contact with the base region. An advantage of the invention is providing a merged BiCMOS device having both PMOS and bipolar devices in the same moat. A further advantage of the invention is providing a merged bipolar/PMOS structure that requires less area. A further advantage of the invention is providing a BiCMOS process that allows for a lower temperature source/drain anneal thereby reducing short channel effects. Details of the invention will be apparent from the following specification in conjunction with the drawings. BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: Figure 1 is a cross-sectional diagram of the preferred embodiment of the invention; Figures 2a-i are cross-section diagrams showing various stages of fabrication of the preferred embodiment of the invention; and Figure 3 is a cross-sectional diagram of an alternative preferred embodiment of the invention. Corresponding numerals and symbols in the different figures refer to corresponding parts unless otherwise indicated. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The preferred embodiment of the invention is described herein as incorporated into a BiCMOS structure having a bipolar transistor and a PMOS transistor merged into the same well region. Figure 1 illustrates, in cross-section, bipolar transistor 60 and p-channel transistors 64 and 68. The structure is formed into a substrate 12 which, in this embodiment, is p-type silicon. Buried n+ region 14 in bipolar transistor 60 serves as a subcollector, in the conventional manner, with n+ region 25 providing a surface contact thereto. N region 18a serves as the collector region in bipolar transistor 60 and as the well region for p-channel transistor 64. N region 18b is the well region for p-channel transistor 68. Intrinsic base 26 is a p-type region disposed within n region 18a-b. Emitter electrode 30 may be a doped polysilicon layer which extends through an opening in insulator layer 24 to intrinsic base region 26. P+ region 52a serves as both the extrinsic base region of bipolar transistor 60 and as one of the source/drain regions for p-channel transistor 64. P+ regions 52 serve as the remaining source/drain regions for p-channel transistors 64 and 68. Doped polysilicon may be used to form gates 40 of transistors 64 and 68. Gate oxide 36 is disposed between gates 40 and n regions 18a-b. Buried region 16 is located below region 20. Field insulating regions 22 isolate intrinsic base region 26 from collector contact 25 and p-channel transistors 64 and 68 from each other. Emitter electrode 30 and gates 40 may optionally be silicided to form TiSi 2 layer 56. N+ regions 14 below transistors 64 and 68 are separated by buried p region 16 and n regions 18a-b are separated by p region 20 to allow the n-type regions 18a-b of the two transistors to be at different potentials. Figure 2a illustrates structure 10 after the formation on n+ buried layers 14, p buried layers 16, n-type regions 18a-b, p-type regions 20, field insulating regions 22, and insulator layer 24. Methods for forming the buried layers are described in U.S. Patent No. 4,958,213, issued September 18, 1990 and assigned to Texas Instruments Incorporated. A method for forming field insulating regions 22 is described in U.S. Patent No. 4,541,167, issued September 17, 1985 and assigned to Texas Instruments Incorporated. Insulator layer 24 may be a dummy gate oxide formed via an oxidation followed by a deglaze to a thickness of less than 20 A followed by a thermal oxidation to a thickness on the order of 300 A. The formation of a merged BiCMOS device according to the invention into the structure of Figure 2a will now be described. The surface of structure 10 is patterned and implanted using a n-type dopant to form a deep n-type region (collector contact 25) that extends through n region 18a to contact the subcollector, n+ region 14, as shown in Figure 2b. Next, the V t adjust implants may be performed: one for NMOS transistors (not shown) and one for PMOS transistors 64 and 68. Still referring to Figure 2b, the base region 26 is patterned and implanted with a p-type dopant (e.g. boron 7.013 cm at 10Kev). Referring to Figure 2c, masking layer 27 is used to expose a region of dummy oxide layer 24. The exposed oxide is then etched to expose a portion of base region 26. Masking layer 27 is then removed and a deglaze is performed (e.g., 10% HF for 10 seconds). Referring to Figure 2d, a layer of conductive material, such as polysilicon layer 29, is deposited to a thickness on the order of 2500 A. Next, polysilicon layer 29 may be doped n-type via ion implantation. Alternatively, the polysilicon may be doped in-situ during deposition. A layer of nitride 32 is deposited over polysilicon layer 29. Nitride layer 32 may have a thickness on the order of 500 Å (10Å = 1nm). Polysilicon layer 29 and nitride layer 32 are then patterned and etched by conventional techniques as shown in Figure 2e to form emitter electrode 30. Nitride layer 32 prevents oxidation of emitter electrode 30 during subsequent processing steps. Referring to Figure 2f, the exposed portions of dummy oxide layer 24 are then removed using a deglaze and replaced with an insulator layer such as gate oxide layer 36. Gate oxide layer 36 is formed by thermal oxidation and has a thickness on the order of 100 A. During the growth of gate oxide layer 36, oxide 37 will also form on the vertical edges of emitter electrode 30 as shown in Figure 2f. The thermal oxidation is performed at a temperature high enough to also serve as the emitter anneal. In the preferred embodiment, the thermal oxidation is performed at a temperature on the order of 900°C. It will be apparent to those skilled in the art that other temperatures, including those used in rapid thermal processing (RTP) may alternatively be used. A second layer of conductive material, such as polysilicon layer 39, is deposited by way of LPCVD over the surface of structure 10, as shown in figure 2f. Polysilicon layer 39 has a thickness on the order of 3500 A. Polysilicon layer 39 may then be doped via ion implantation. Alternatively, the polysilicon may have been doped in situ during deposition. Polysilicon layer 39 is patterned and etched to form gates 40, as shown in Figure 2g. Referring to Figure 2h, conventional techniques are then used to implant lightly doped drains (LDDs) 44, form sidewall spacers 48, and form source/drain regions 52 and 52a. It should be noted that LDDs 44 are optional and need not be formed. Sidewall spacers 48 are formed by depositing a dielectric layer and anisotropically etching the dielectric layer. Sidewall spacers 48 may be oxide or oxide/nitride. It should be noted that the anisotropic etch used to form sidewall spacers 48 also removes nitride layer 32 and may remove exposed portions of gate oxide layer 36. After sidewall spacers 48 are formed, source/drain regions 52 and 52a are implanted and annealed. It should be noted that source/drain region 52a also serves as the extrinsic base of the bipolar transistor. Because the doped emitter electrode was previously "annealed" during the formation of oxide layer 36, source/drain regions 52 and 52a may be annealed at lower temperatures (on the order of 850°C) thereby reducing short channel effects. Subsequent to the processing steps described above, the gates 40, source/drain regions 52 and 52a, and emitter electrode 30 may optionally be silicided. A layer of refractory metal (not shown) is deposited over the surface of structure 10. The structure is annealed using a rapid thermal anneal, or alternatively a furnace anneal, in a nitrogen-containing ambient. This causes the layer of refractory metal to react with any exposed silicon to form silicide. Referring to Figure 2i, silicide layer 56 is formed above emitter electrode 30, gates 40 and source/drain regions 52 and 52a. Elsewhere, a layer of refractory metal-nitride and/or unreacted metal (not shown) is formed. The layer of refractory metal-nitride and/or unreacted metal is then removed. Subsequent to the completion of the methods described above, interconnecting metallization is then formed for making contact to the active regions of Figures 1 and 3. Methods for forming such interconnections are well known in the art. Individual circuits are then separated from portions of substrate 12 and external connections made thereto by way of wire bonding, direct bump bonding, or the like, as is well known in the art. The individual circuits may then be packaged into a dual-in-line package, a chip carrier, or another type of package. An example of such a package is described in U.S. Patent No. 4,495,376 issued January 22, 1985 and assigned to Texas Instruments, Inc.

Claims: A method for forming a BiCMOS device comprising the steps of: forming a first insulator layer (24) over a surface of a semiconductor body having a first well region (18a); then, implanting a base region (26) in a first portion of said first well region (18a); then, forming an emitter electrode (30) over said first insulator layer (24) and said base region (26), wherein a portion of said emitter electrode extends through said first insulator layer (24) to said base region (26); then, removing a portion of said first insulator layer (24) not covered by said emitter electrode (30); then, growing a second insulator layer (36) on the surface of said semiconductor body, wherein said growing step also serves as an emitter anneal; then, forming a plurality of gate electrodes (40) on said second insulator layer (36), wherein at least one of said gate electrodes (40) is formed over said first well region (18a); and then, forming a plurality of source/drain regions (52) at a temperature less than 900°C at the surface of said semiconductor body, wherein a first one of said source/drain regions (52a) is formed between said at least one gate electrode (40) and said emitter electrode (30), said first source/drain region (52a) contacting said base region (26). The method of claim 1, wherein said step of forming said emitter electrode (30) comprises the steps of: etching said first insulator layer (24) to expose a portion of said base region (26); forming a first doped conductive layer (29) over the surface of said semiconductor body; depositing a nitride layer (32) over said first conductive layer (29); and etching said nitride layer (32) and said first conductive layer (29) to form said emitter electrode (30) and to expose a portion of said first insulator layer (24). The method of claim 2, wherein said step of forming said gate electrodes (40) comprises the steps of: forming a second doped conductive layer (39) over the surface of said semiconductor body; and etching said second doped conductive layer (39) to form said plurality of gate electrodes (40). The method of claim 3, further comprising providing said first and second doped conductive layers (29, 39) by polysilicon implant doping after the deposition step. The method of claim 3, further comprising providing said first and second doped conductive layers (29, 39) by polysilicon doping in situ. The method of any preceding claim, further comprising growing said second insulator layer (36) at a temperature of greater than about 850°C. The method of any preceding claim, further comprising the steps of: implanting lightly doped drains (44) on opposite sides of each gate electrode (40) after said step of forming said gate electrodes (40); and forming sidewall dielectrics (48) adjacent each of said gate electrodes (40) and said emitter electrode (30). The method of any preceding claim, further comprising the step of siliciding said emitter electrode (30) and said gate electrodes (40). The method of claim 8, wherein said step of siliciding said emitter electrode (30) and said gate electrodes (40) comprises the steps of: depositing a layer of refractory metal over the surface of said semiconductor body; annealing said layer of refractory metal in a nitrogen containing ambient to form a layer of silicide (56) over said emitter electrode (30) and said gate electrodes (40) and a layer of refractory metal-nitride or unreacted metal where said silicide layer is not formed; and etching said layer of refractory metal-nitride or unreacted metal. The method of any preceding claim, wherein said step of forming said source/drain regions (52, 52a) comprises the steps of: implanting said source/drain regions (52, 52a); and annealing said source/drain regions (52, 52a) at a temperature less than 900°C. The method of any preceding claim, further comprising forming said first insulator layer (24) comprising oxide in the order of 30 nm (300 Å) thick and forming said second insulator layer comprising oxide in the order of 10 nm (100 Å) thick.

Inventors: EKLUND ROBERT H, EKLUND ROBERT H.
Applicants: TEXAS INSTRUMENTS INC, TEXAS INSTRUMENTS INCORPORATED
Application year: 1994
Main classification: H01L27
IPC codes: H01L21, H01L29, H01L27